Method of making dentures



Jan. 23;, 1945. d E. H.- GAL 2,367,767

METHOD OF MAKING DENTURES Filed Jan. 2'7,l 1940 4 Wag;

70 J-I'IIII|I||||||||||||||||"um" Patented Jan. 23, 1945 UNITED STATESPATENT OFFICE METHOD F MAKING DENTURES Edward Il. Gale, Chicago, Ill.

Application January 27, 1940, Serial No. 315,947

i Cl. 18-55.1)

2 Claims.

This invention relates to a method of molding dentures comprisingunplasticized acrylic resins without tin-foiling the mold.

Heretofore all acrylic resins molded into dentures have been plasticizedbefore molding. The resulting plasticizer content of the acrylic resinsentails serious disadvantages, which have hereccfore been thought to beinherent characteristics of acrylic resins. It is necessary, forinstance, to seal the porous plaster molds used against entry ofmoisture by lining the same with tin foil, as access of even a trace ofmoisture to the plasticized resins during molding would discolor the'iinished dentures badly. The formation of bubbles in dentures is alsoprobably due to the presence of plasticizers in the resins. Denturesprepared from plasticized acrylic resins are further incapable of beingsterilized in boiling water, beh-1g liable to warp even at thetemperatures and under the moisture conditions prieveilinfg in oralcavity.

he appended drawing illustrates the methods te present invention formolding unplastiacrylic resins without tin foiling the mold.particularly:

Figure l is a transverse cross-Sectional view ci a female impression ofthe toothless gums and palate of an upper jaw as made by a denis atransverse cross-sectional view 'ruotare representing an intermediatestage pai-ation or" a plastermcld for unplasee. lic resins not to belined with tin `ifi-ure 3 is a perspective view ci the inside of theupper half of a plaster mold for unplastisized acrylic resins not linedwith tin foil.

Figure ci is a transverse cross-sectional View of a plaster mold notlined with tin foil packed with an unplasticized acrylic resin.

Figure 5 is a fragmentary greatly enlarged crcsssectional View of agranular unplasticized acrylic resin packed in a plaster' mold not linedwith tin fell.

The following description of the conventional method of molding an upperdenture from plasticized acrylic resins will show the relativeimpertence and cost cr the tin oiling operation es compared with theother steps o this process.

i conventional molding method startsI with a female impression of thetoothless gums and hard palate of the upper jaw made by the dentist.Such a female impression is illustrated in Figure l and there designatedwith the reference numeral iii.

From this female impression a male mold in hard dental plaster isprepared. The concavity of this male mold corresponding to the hardpalate and the ridges duplicating the toothless gums'are then covered tosuitable depths with wax and teeth are set into the wax on the ridges inproper alignment and with proper projections from the wax. The surfaceof the wax is then shaped manually or with a suitable instrument toconform to the contours of a normal hard palate end of normaldentigerous gums. The thus prepared and waxed male mold together withthe teeth aligned thereon is known as a waxed up denture.

The Wax of the waxed up denture together with thereto adjacent marginalparts of the male mold and teeth are then covered with tin foil and thelatter is burnished so as to close all openings in the tin foilincluding the most minute pores and pinholes.

The waxed up denture, with its tin-foiled side up, is then placed in therelatively wider and shallower cup formed by the lower portion of aiiask and invested there with plaster. The tinfoiled portion of thedenture projects above the edge of the bottom portion of the ask. Theannular top of the plaster surrounding the waxed up denture is trimmedilush with the edges of the tin foil, and separating :duid is applied tothe top surface of the trimmed plaster, to prevent adhesion ofadditional plaster to be applied thereon in a subsequent step.

The upper `open-topped portion of the flask is then put in place overthe lower portion of the flask, and the flask is completely iilled withplaster which covers the trimmedv surface of the investing plaster inthe lower portion of the flask, the tin-foiled waxed portion of thewaxed up denture and the teeth projecting from the waxed ridges of thedenture. When this plaster hardens, it grim the teeth projectingthereinto and the tin ioil also adheres thereto.

The lid of the ask is then put over the upper portion of the liask andtapped down lightly. The ilaslr is immersed in boiling water :for l5 to20 minutes to melt and remove the wax. The removal of the wax leaves acavity between the upper surface of the male mold invested in the lowerportion of the ask and the tin-foil covered lower -surface of theplaster in the upper portion of the ask which plaster is separable fromthe investing plaster in the lower portion of the flask. 'I'he rootportions of the teeth held by the plaster in the upper portion of theflask project through the tin foil into this cavity.

The upper and lower portions of the flask together with plaster adheringto eachare then separated. Residual wax is removed from the cavity withhot water. That portion of the surface of the male mold which had beencovered with wax and surfaces adjacent thereto are then covered with tinfoil and the latter is burnished. The final result is a two-memberedplaster mold or case whose molding surfaces are lined with a moistureproof layer of burnished tin foil.

Acrylic resins for use in conventional molding processes are availableboth as plasticized sheets and as granular products which are intermixedwith plasticizer and worked with a pestle in a mortar to form a plasticmass immediately before use.

Such acrylic resins which according to conventional methods invariablyare plasticized in one way or another are packed in the cavity oi' thecase lined with tin foil. The case is then placed in a hand press andexposed to heat and pressure in the presence of moisture for a suitablelength of time. The mold is then cooled, taken apart, and the dentureremoved therefrom.

The total time required for manipulation in the conventional moldingprocess amounts to from 1 hour and 30 minutes to 1 hour 'and 40 minutes.The tin-foiling and burnishing step requires from 20 to 40 minutes ofthis time.

The present invention departs radically from the teaching of the priorart that acrylic resins must be plasticized for denture molding purposesby providing a method of molding dentures from unplasticized solidacrylic resins. This process, contraindicated by the prior art, has thesurprising eilect of rendering unnecessary the tin-foiling step thoughtby the prior art to be an unavoidable handicap to the molding ofdentures from acrylic resins and yields also, contrary to what the priorart thought possible, a denture characterized by such resistance tomoist heat as to be capable of being sterilized by immersion in boilingWater. Methods accordingr to the present invention further includeoptional employment of dry heat in molding, involving ternperatures andpressures far in excess of those previously employed, but still notaccompanied by the cracking or checking of the teeth of the dentureswhich occurred at the -lower temperatures and pressures of the prior artmethods. Dentures prepared according to the present invention aremoreover distinguished by great density and mechanical strength. Suchdentures. for instance, may be dropped without danger of breaking. As amatter of fact. the unplasticired acrylic resin is so tough as to bemore resistant to mechanical shocks than the porcelain teeth of thedenture.

The present invention further provides methods of molding dentures fromunolasticized acrylic resins without the use of tin foil involving thewetting of the resins with relatively volatile and inert liduids whichat ordinary temperatures do not render the resins plastic. Carbontetrachloride is a typical example of such a liouid. the use of whichmakes it possible to mold unplasticized acrylic resins at lowertemperatures and pressures than otherwise neces- Sary.

It is therefore an important object of the present invention to providea method of making dentures comprising unplasticized acrylic resins.

Another important object of this invention is to provide a method ofmolding dentures from acrylic resins in plaster molds withouttin-foiling the molds used.

Yet another object of the invention is to provide a method of moldingdentures from acrylic resins wetted by relatively volatile and inertliquids incapable of plasticizing said resins at ordinary temperaturesastypified by carbon tetrachloride.

Other and further important objects of the present invention will becomeapparent to those skilled in the art from the following description andthereto appended claims.

The principles of the present invention are illustrated by the followingexamples of practical embodiments thereof. Numerous other applicationswill suggest themselves to those skilled in the art.

Exim/irma` I Warm pack; semi-dry heat cure A waxed up denture isprepared according to the conventional method but the denture is nottin-foiled. This waxed up denture is invested as described hereinabove,the investing plaster being trimmed flush with the edges of the wax, anda plaster impression thereof is made by the use of the open-toppedportion of the flask as also described hereinabove.

Figures 2, 3, 4 and 5 illustrate specific methods of this example andshow a male mold 20, wax '2 I, teeth 22, a lower portion 24 of a flask,plaster 25 in this lower portion 24 having a trimmed top surface 26, anupper portion 21 of the same flask, plaster 28 in this upper portion 21,and

a lid 29 for the flask.

The wax is eliminated from the two-membered mold or case thus obtained,the cavity is washed with acetone, and ve or six spaced waste gates 4Uare provided in'the mold by cutting registering small recesses in andacross the facing edges of the two plaster casts. These waste gates openinto the cavity of the mold. The male mold is not tin-foiled after theelimination of the wax.

The acrylic resin employed is the polymerized acrylic ester known underthe trade name Crystalite M- and is sold by Rohm and Haas Co., Inc., ofPhiladelphia, Pennsylvania. This resin is distinguished by a specificgravity of 1.18 to 1.19, a specific heat of 0.4 to 0.5 calories perdegree of centigrade per gram, and a refractive index of about 1.49.

One ounce of suitably dyed or pigmented granular Crystalite M-lOO ismixed with one-half ounce of carbon tetrachloride until the resingranules are thoroughly wetted and the mixture has the consistency ofwet sand. The carbon tetrachloride not adsorbed on the resin particlesas a wetting coating collects on the bottom of the container.

While the flask is still warm, the cavity in the plaster in theopen-topped portion of the flask is packed full with resinous granules4| (Figure 5) wetted with carbon tetrachloride which are pastified atthe temperature of the mold. 'I'he pastied resin is designated in Figure4 by the reference numeral 42. A sheet of wet Cellophane is optionallyplaced over the resin, to make the upper surface of the denture smooth.The male die is put in place, the flask, which should still be warm, isassembled and put in a hand press. The press is tightened slowly, toavoid. losses of material from the cavity by the gushing out of carbontetrachloride through the waste gates. The flask is then put in a dryheat electric press under a slowly increasing pressure. When after about20 minutes carbon tetrachloride vapors and steam cease to escape throughthe waste gates, the full pressure of the press is turned on, so thatthe aslt is completely closed. The ilasl; is kept under a pressureamounting to upwards of 3000 pounds at a temperature of about 300 F.for, say, 20 minutes. The ilask is then removed from the electric press,placed in a hand press, allowed to cool somewhat, immersed in coldwater, and the denture is removed and nished.

While the flask is in the electric press, the acrylicresin is moldedinto the desired shape and all carbon tetrachloride is eliminatedtherefrom. 'in spite or the absence of tin foil and the tree access ofmoisture adsorbed by the porous plaster mold, the resulting denture isnotv discoiored and is free from bubbles. The denture is `further muchstronger mechanically than prior art dentures molded from plastlcizedacrylic resins, not given to warping and capable ofr being sterilized byimmersion in boiling Water.

This particular method is designated as involving semi-dry heat and hotpacking as a moderate amount of moisture is present in the mold duringthe heating step and the resin is packed into the mold while the latteris hot, the wetted resin being pasty at this elevated temperature.

EXAMPLE II Warm pack; hot water cure A mold is prepared as in Example I.While the mold still is warm,`the mold cavity is packed with suitablypigmented or dyed granular acrylic resin Crystalite lvl-100 which hasbeen 'wetted with a mixture of 80 per cent carbon tetrachloride and 2oper cent acetone t'o form a mass having the consistency of Wet sand. Asheet of Cellophane can be placed over the resin before male mold istelescoped thereinto. The mold flask is inserted in a hand press andimmersed in a vessel or" boiling water for about 40 minutes. The flashis then removed from the vessel, cooled, opened and denture removed.

rlhe resulting denture is not discolored, is free from bubbles, iscapable of being sterilized by immersion in boiling water and isdistinguished by great mechanical strength.

EXAMPLE lll Warm pack; dry heat curev A mold is prepared as in Examplel' and thereafter dehydrated thoroughly by suitable heating. While moldis still warm, the mold cavity packed with suitably pigmented or dyedgranular lacrylic resin such as Crystalite l -100. The male mold istelescoped into the mold cavity, the flask is assembled and insertedinto an electric press and there exposed to a tempera- 'ture of about340" F. to 360 F. and a pressure of upwards of 3000 pounds for aboutminutes. The flask is then removed from the electric press, placed in ahand press and then cooled. The denture is removed after cooling iscomplete.

'lhe resulting denture is not discolored, is free from bubbles, iscapable of being sterilized by immersion in boiling water and isdistinguished by exceptional density and mechanical strength.

As shown by these examples, the present invention comprises the moldingof unplasticized granular masses of acrylic resins. These unplasticizedmasses may be treated with liquids that wet the granular' resins andwhile not rendering the resins plastic at ordinary temperatures stiliserve to lower the temperature at which the resins turn pasty. Theseliquids are herein designated as "pastifying liquids. 'I'he aboveexamples mention the following pastifying liquids: carbon tetrachloride,a mixture of 20 per cent acetone and 80 per cent carbon tetrachloride.Other pastifying liquids include mixtures of l0 per cent butyl acetateand 90 per cent carbon tetrachloride, of 10 per cent toluene and 90 percent carbon tetrachloride, oi 10 or ai) per cent trichlor ethylene and90 or 30 per cent carbon tetrachloride, of 50 per cent acetone and 50per cent carbon tetrachloride and many others. Straight ethyl ether istoo volatile while toluene per se is not volatile enough. In general,pastifying liquids according to this invention include non-polymerizableliquids which do not render acrylic resins plastic at ordinary roomtemperatures, which are not so volatile as to be eliminated prior to theheat cure, but which are suilclently volatile to be eliminatedcompletely during the heat cure and which serve to make acrylic resinspasty at elevated temperatures.

The function of the pastifying liquids is shown more clearly by the coldpack molding methods of this invention. ln these methods the moldprepared as in Example l is allowed to cool before the resin wettedwith, say, carbon tetrachloride is packed in the mold cavity. The wettedresin ,is placed in a glass vessel and the vessel is dipped in hotwater, whereby the resinous mixture is made pasty. The pasty resin isthen packed in the mold cavity and molding is carried out as in Examplel.

In molding, high temperature may compensate for less intense pressure,and vice versa. while a prolonged less intense treatment may besubstituted for a shorter more intense treatment.

While this invention is applicable to acrylic resins proper whichinclude the resinous polymerization products of acrylic acid and itsesters, and, in particular, to the polymerized esters, the invention isparticularly applicable to the resinous polymerization products ofmethacrylic acid and its esters. The term acrylic resin as used hereindesignates both acrylic acid and metha crylic acid derivatives.

The present invention may therefore be broad- 'ly characterized ascomprising the molding of dentures of unplasticized acrylic resins andmethods ci preparing such dentures including molding unplastioizedacrylic resins in plaster molds immediately contacted by the moldedresin, thus eliminating the conventional tinfoiling of plaster molds.The molding according to this invention also includes optional use ofpastifying liquids.

The prior art is familiar with the molding of acrylic resins in metallicmolds and, in the case of molded dentures, with the molding of acrylic fresins in molds lined with burnished tin foil. IThe present invention,on the other hand, presents a radical innovation in the art of moldingacrylic resins by providing molding methods in which the acrylic resinsare exposed to the action or" heat and pressure while in immediatecontact with the Walls of porous plaster molds permitting the access cimoisture.

As pointed out hereinabove, various details of the present invention maybe varied through a wide range without departing from the principles ofthe invention and it is, therefore, not the purpose to limit the patentgranted hereon 4 asomo? otherwise than necessitated by the scope oi theappended claims.

I claim as my invention:

1. In a method of making a. molded denture which comprises subjecting anacrylic resin to the action of heat and pressure in immediate contactwith a plaster mold, the step comprising wetting said resin with carbontetrachloride before subjecting said resin to said action of heat andpressure.

2. In a method of making a molded denture which comprises subjecting anacrylic resin to the action of heat and pressure, the step comprisingwetting said resin with carbon tetra.- chloride before subiecting saidresin to said action of heat and pressure.

EDWARD H. GALE.

